Money well spent. It's held good value over the years. Please post a link to the article. Thanks.

The Carver Challenge was posted to our homepage yesterday.

Where is that original modified Carver amp today?

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Where is that original modified Carver amp today?

Bob Carver took it back with him when the Challenge was over, where it was used as the prototype for the M1.0t amplifier that was released in 1986. Stereophile reviewed this model in April 1987 (review not yet posted in our archives) and found that it neither measured nor sounded like the C-J tube amp of which it was supposed to be a clone. The null I measured between the production M1.0t and the tube amp using the same methodology as Bob Carver was just 36dB and then only in the midrange.

John Atkinson
Editor, Stereophile

First let me say that while no fan of Carver amps, Carver deserves every bit of respect for being able to do what he did (and if he can do what he did with any amp, it isn't theft in my book, nor should it be illegal, if the amp is sold on the open market). But if Carver had the modified amp to model on, I don't get why he was not able to duplicate modified 1.0's. He would have made a bazillion dollars off this thing, and at say, $1k a pop, I would have been his first customer.

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But if Carver had the modified amp to model on, I don't get why he was not able to duplicate modified 1.0's. He would have made a bazillion dollars off this thing, and at say, $1k a pop, I would have been his first customer.

The tweaking that he must have been doing with those trim pots was subtle enough that even small variations in the electrical values of individual samples of parts would have thrown off the results when talking about a mass produced product. He probably COULD have used trim pots in the mass produced versions and "tuned" every amplifier separately off of the line but that would have increased both parts and labor costs.

While I agree that it was an impressive technical accomplishment what Mr Carver did so is creating a fake painting good enough to fool a good number of experts. Would it legally speaking be criminal to sell them? As the article states probably not. Would it be morally wrong? I'd go with yes, on some level it is. I can't explain it but "stealing" the sound of someone else's design and "trapping" it in your metal box feels almost like stealing the soul of a living creature and trapping it elsewhere. I know that sounds overly dramatic but that's how I feel. Truly high-end components (not determined by price) are works of art that ALMOST have a soul.

As I recall, the tube amplifier drifted from the first time that he performed the null. Most likely due to the tubes aging. I don't recall where I read this, but I'm fairly certain that this was the issue.

Also, as I recall, his final tuning was to limit the power of his amp, and add some distortion to improve the match.
He might have left out the power limiting and extra distortion in production to have something similar but slightly better.
Speculation on my part, anyone know the facts?
Link to a .pdf version of the article:
http://www.carveraudio.com/CarverChallenge.pdf

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As I recall, the tube amplifier drifted from the first time that he performed the null. Most likely due to the tubes aging. I don't recall where I read.

Following publication of the 1987 Stereophile review of the M1.0t, Mr. Carver made this claim in several places, such as Larry Klein's column in Radio & Electronics. It was not correct.

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his final tuning was to limit the power of his amp, and add some distortion to improve the match.
He might have left out the power limiting and extra distortion in production to have something similar but slightly better.

Speculation on my part, anyone know the facts?

Not to my knowledge. A primary difference between the production M1.0t and the reference tube amplifier was that the Carver was actually better at low frequencies. In the 1987 series of blind tests, Mr. Carver added about 15' of small-gauge cable in series with the M1.0t's output to reduce the damping factor and make the amplifiers sound more similar. He did incorporate a switchable series resistance in subsequent production, I believe.

John Atkinson
Editor, Stereophile

Just the 1 percent feedback resistor tolerances of the transistor amp will be enough to wipe out the 70 dB null, making it 40 dB or less. A pot would be required for a 70 dB null. I seriously doubt if any two C-J amps of the same type could have such a null between each other, just because of the gain mismatch. Stereophile's measurement data regularly show channel-to-channel gain mismatches of a given amp on the order of tenths of a dB, which will wipe out a 70 dB channel-to-channel null right there.

Good point Andy, I don't know their exact procedure however I would expect some sort of null balance control to at least remove small gain differences.

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I seriously doubt if any two C-J amps of the same type could have such a null between each other, just because of the gain mismatch.

You do have to adjust for the gain difference in such a null test, which is what I did back in 1987. But the important point to note is that with 2 nominally identical amplifiers (ie, samples of the same design), the null should not vary significantly with frequency, whereas with the Carver-vs-CJ null that I measured, the shape of the null-vs-frequency curve was a V, ie, very limited nulling at the frequency extremes, increasing to a maximum null somewhere in the upper midrange.

John Atkinson
Editor, Stereophile

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...the shape of the null-vs-frequency curve was a V, ie, very limited nulling at the frequency extremes, increasing to a maximum null somewhere in the upper midrange.

Do you suppose that less null at frequency extremes may also mean less detectability by the ear, so that the null is effectively better than the numbers indicate?

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...the shape of the null-vs-frequency curve was a V, ie, very limited nulling at the frequency extremes, increasing to a maximum null somewhere in the upper midrange.

Do you suppose that less null at frequency extremes may also mean less detectability by the ear, so that the null is effectively better than the numbers indicate?

No, because the area where the two amplifiers sounded quite different was in the low frequencies, where the null was relatively small.

John Atkinson
Editor, Stereophile

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...the shape of the null-vs-frequency curve was a V, ie, very limited nulling at the frequency extremes, increasing to a maximum null somewhere in the upper midrange.

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Do you suppose that less null at frequency extremes may also mean less detectability by the ear, so that the null is effectively better than the numbers indicate?

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No, because the area where the two amplifiers sounded quite different was in the low frequencies, where the null was relatively small.

John Atkinson
Editor, Stereophile

I was thinking that the ear is less sensitive to volume at low and high frequencies. But since the null is less there, it should be more easily detected than at the mid-frequencies (of course, because less null means more different). Also, you probably would not be litstening at lower volume levels, so the loudness curve I was thinking of doesn't even enter into it.